Silk is a natural material with excellent thermal resistance and mechanical properties and has traditionally been utilized primarily in textile applications. Direct incorporation of silk into polypropylene (PP) via injection molding has raised concerns regarding the formation of agglomerates (lumps) due to inadequate dispersion. In polymer compounding, it is well established that the addition of substances such as water can enhance the dispersibility of additives within the resin matrix. Recent studies have also reported that silk, when exposed to temperatures exceeding 170 °C, undergoes dehydration-induced thermal decomposition, resulting in the generation of superheated vapor. In this study, we aimed to suppress the formation of silk agglomerates by leveraging the superheated vapor generated from silk, thereby enhancing the thermal and mechanical performance of the resulting composite. These results demonstrated that silk was uniformly dispersed within the PP matrix, leading to the desired enhancement in composite properties. The key to achieving this outcome was the optimization of the compounding temperature to 210 °C. Notably, silk exhibited the capacity to retain water up to this elevated temperature, effectively functioning as an intrinsic “water reservoir.” This finding reveals a novel characteristic of silk that contributes to its potential as a functional additive in polymer composites.

View full abstract

The cocoon fiber of Bombyx mori strain F7 features significant fine fibers with irregularly shaped fibroin. We treated cocoon fibers with lithium bromide to swell the fibroin for observation. Optical microscopy revealed linear grooves on the sides of the fibroin. SEM images of fiber cross-sections showed that these grooves were abnormal structures associated with the depression of the fibroin surface. The grooves were present in the outer to middle layers of the cocoon, but not in the inner layers. Slight depressions in the outer layer appeared to indicate the early stage of the structure. On the other hand, fibroin in strain CV, which does not produce the fine fibers, had no grooves. These results suggest that the depression is specific to F7 and may be fundamental to the development of the fine fibers. The F7 fibroin was severely split by the linear grooves, indicating that structural defects may be latent in the fibroins of strains that generate fine fibers.

View full abstract

It is possible to produce highly functional silk by expressing recombinant fibroin fusion proteins in silk glands via gene modification technology. Fluorescent silk is engineered by expressing fluorescent proteins fused with fibroin in silk filaments. Currently, several fluorescent silk varieties are available for industrial use. In this study, to investigate the effect of fluorescent silk on color mixing, we hybridized a blue fluorescent silk-producing strain (emitting under ultraviolet light) with orange, green, and red fluorescent strains to investigate changes in silk characteristics, such as fluorescent color shifts. The results showed that crosses between the blue and green strains produced green silk fluorescing at ultraviolet wavelengths not normally excited. In contrast, no synergistic effect was observed in crosses between blue and orange strains. Multiple fluorescent silk-producing strains have been developed for this purpose. Hybridizing them to stack protein genes broadens their potential applications.

View full abstract

Hornet silk (HS) collected from hornet nests can be processed easily into a regenerated film through dissolution into a concentrated salt solution, followed by desalting and drying. In fact, HS requires no pre-dissolution refining. Moreover, dissolution processes can be performed at room temperature. Although the risk of protein degradation caused by heating during processing is low, the actual degradation effects remain unclear. Results of detailed SDS-PAGE analyses of cocoons and regenerated films conducted for this study confirmed that part of Vxsilk4 (x = s, a), a major protein constituting HS, was degraded in regenerated films prepared from cocoons of Vespa simillima and Vespa analis. The addition of PMSF, a specific inhibitor of serine proteases, inhibited this degradation, suggesting that enzymes present in the nest or cocoon acted during film fabrication. By contrast, no similar protein degradation was observed in a film prepared from a Vespa mandarina cocoon.

View full abstract

In recent years, Japan’s silk industry has been in a steady decline due to an aging workforce and a lack of successors. To address this issue, it is essential to establish an industry–academia–government consortium in which organizations involved in the silk industry can work together to examine current challenges. This paper focuses on the project “Advocating the Role of silk Art and Cultural heritage at National and European scale” (ARACNE), a collaboration among silk industry-related organizations in Europe. ARACNE was established in 2023 mainly by the Council for Agricultural Research and Economics (CREA) in Italy, with funding from the European Union’s research and innovation program “Horizon Europe.” Designed to revitalize the silk industry, ARACNE works with silk-related manufacturing companies, research organizations, and educational institutions to build an ecosystem in Europe through information collection and educational activities focused on the cultural heritage of the European silk industry. This paper summarizes the activities of ARACNE and the background of its establishment and considers the possibility of establishing an industry–academia–government consortium in the Japanese silk industry.

View full abstract